1. Field of the Invention
The present invention relates to controllers for front wheel drive vehicles. More particularly, the present invention relates to such controllers configured to control a front wheel drive vehicle in dependence on acceleration measurements.
2. Description of the Prior Art
Front-wheel drive motorised vehicles, for example motorised electric wheelchairs, that employ independently driven left and right wheels are extremely manoeuvrable. However, this type of vehicle is prone to spinning out of control when cornering at speed because its centre of mass is located behind the drive wheels. This problem may be particularly acute in the example case of an electric wheelchair having free-rotating casters that support the rear of the vehicle since these provide very little resistance to any rotational forces acting on the wheelchair's centre of mass.
In this example, when the wheelchair starts to corner at a given forward velocity, the centripetal acceleration acting on the centre of mass increases in proportion to the forward velocity squared, divided by the cornering radius of the wheelchair. The resulting centripetal force pushes the trailing centre of mass outwards causing the rear of the wheelchair to swing out and hence the drive wheels begin to slip. The free-rotating casters at the rear of the wheelchair provide very little resistance to this twisting force and the rear of the wheelchair begins to spin out causing the user to lose control of the wheelchair. During the spin out, the centripetal acceleration acting along the lateral axis of the wheelchair mass begins to be transferred to the forward axis of the wheelchair as the wheelchair starts to rotate more about the centre axis of its drive wheels.
Various known controllers for vehicles such as electric wheelchairs are described in US Patent Application Publications 2010/011443 and 2010/0174432, JP Patent Application Publication 2010/193939A and U.S. Pat. No. 6,202,773.
It would be desirable to provide an improved controller which addresses the above discussed problems.